Fennel (Foeniculum vulgare) is a native plant of the Mediterranean region. The bulbs, leaves, and seeds are commonly eaten. Fennel has a mild licorice flavor and celery-like texture. It is a good source of potassium.

Fennel fruits have been used as a traditional herbal medicine in Europe and China. Fennel tea has been used as a remedy to treat indigestion in infants.

Good human evidence suggests that fennel reduces colic in infants. According to limited human evidence, fennel may also reduce painful menstruation and protect against damage caused by ultraviolet light. Fennel tea alone or in combination with other herbs is popularly used for gastrointestinal disorders and to improve digestion. However, studies evaluating fennel alone for this use in humans are needed.

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

GRADE *

Limited research suggests that fennel may reduce infantile colic. Additional studies are needed to confirm these promising findings.

B

Preliminary evidence suggests that fennel may help relieve a cough from using certain blood pressure-lowering drugs called ACE inhibitors (ACEI). However, there is insufficient evidence to make a conclusion for or against its use for ACEI-induced cough.

C

According to preliminary evidence, fennel, when combined with other herbal agents, may decrease pain associated with colitis (inflammation of the colon). More evidence is needed before further conclusions can be drawn.

C

Evidence evaluating the effects of fennel combined with other herbal agents suggests that it may reduce constipation. Studies evaluating fennel alone are needed before further conclusions may be drawn.

C

Fennel has been used to treat painful menstruation. Although preliminary research is promising, further research is needed before conclusions can be drawn.

C

Fennel has been studied in women with hirsutism (excessive facial and body hair), due to its estrogenic effects. More research is needed before further conclusions can be drawn.

C

According to preliminary evidence, sweet fennel combined with other aromatherapy agents may reduce nausea in patients in hospice programs. More evidence is needed before a conclusion can be drawn.

A: Strong scientific evidence for this useB: Good scientific evidence for this useC: Unclear scientific evidence for this useD: Fair scientific evidence for this use (it may not work)F: Strong scientific evidence against this use (it likley does not work)

Tradition / Theory
The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.

For general use as a tea, 1-2 grams of crushed or ground fruit or seed may be added to 150 milliliters of boiling water for 5-10 minutes and strained. One cup of tea has been taken by mouth three times daily. As an antioxidant, doses of 205, 700, and 4,600 micrograms of aqueous extract taken by mouth have been suggested.

For angiotensin converting enzyme (ACE) inhibitor-induced cough, 1-1.5 grams of fennel fruit has been taken by mouth up to three times daily.

For painful menstruation, 25 drops of a 2% concentration of fennel fruit has been taken by mouth every four hours for five days. Thirty drops of fennel every six hours for the first three days of menses have also been taken by mouth, as has 46 milligrams of fennel, taken at the onset of pain or bleeding, five times daily for three days.

For stomach discomfort, 0.1-0.6 milliliters of fennel oil, 5-7 grams of fennel seed, 10-20 grams of fennel syrup and honey, or 5-7.5 grams of tincture has been taken by mouth daily. One to three grams of fennel in 150 milliliters of infusion, 1-3 milliliters of fluid extract 1:1 (grams per milliliter), or 5-15 milliliters of fennel tincture 1:5 (grams per milliliter) have been taken 2-3 times daily between meals. Also, 0.2-0.7 grams of dry extract of fennel 3.9-4.9:1 (weight/weight) has been taken 2-3 times daily.

For inflammation of mucous membranes in the upper respiratory tract, 0.1-0.6 milliliters of fennel oil (equivalent to 0.1-0.6 grams of herb), 5-7 grams of fennel seed, 10-20 grams of fennel syrup or honey, or 5-7.5 grams of tincture has been taken by mouth daily. One to three grams of fennel infusion in 150 milliliters of water, 1-3 milliliters of fluid extract (1:1 grams per milliliter), 5-15 milliliters of tincture 1:5 (grams per milliliter), or 0.2-0.7 grams of dry extract 3.9-4.9:1 (weight/weight) has been taken by mouth 2-3 times daily between meals.

For excess hair growth, 1% and 2% fennel cream has been applied to the skin twice daily for 12 weeks.

For ultraviolet protection, 2% and 5% naturally active botanical fennel have been used in an emulsion on the skin.

Children (under 18 years old)

For colic in infants 2-12 weeks old, 0.1% fennel seed oil in a water emulsion and 0.4% polysorbate-80 has been used for one week.

For inflammation of mucous membranes in the upper respiratory tract, 0.5 grams of the oil per kilogram of body weight has been used. For children aged 1-4 years, 3-6 grams of fennel has been used daily; for those aged 4-10 years, 6-10 grams has been used daily.

Safety
The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

Avoid in individuals with a known allergy or hypersensitivity to fennel or other members of the Apiaceae family, including anise, carrot, celery, and mugwort, because of the chance of cross-sensitization. Severe laryngeal swelling, bronchial asthma, hives, or allergic shock may occur. Oral allergy syndrome has been reported with the use of fennel in a woman. Allergic reactions affecting the skin such as atopic dermatitis (chronic skin inflammation) and light sensitivity may occur in patients who consume fennel. Fennel has been reported to provoke reactions in children with food allergy.

Side Effects and Warnings

Fennel seed is likely safe when consumed by mouth by nonallergic individuals in amounts typically found in food. Fennel and fennel tea are generally well tolerated. Allergic reactions and gastrointestinal discomfort are the most common adverse effects, but rarely occur. Fennel oil has Generally Recognized as Safe (GRAS) status for food use in the United States.

Side effects may include an effect on activity of the sympathetic nervous system when the essential oils are inhaled, gastrointestinal complaints, increased menstrual flow, methemoglobinemia (a blood disorder) in infants following ingestion, epileptic seizures with the use of fennel oil, bronchial asthma, hay fever, occupational rhinoconjunctivitis, asthma, and premature breast development in females. In an adult female, severe iron deficiency and problematic upper gastrointestinal irritation developed following the ingestion of pan masala that included fennel seed and betel nut.

Fennel may increase the risk of bleeding. Caution is advised in patients with bleeding disorders or those taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.

Fennel may lower blood sugar levels. Caution is advised in patients with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

Use fennel honey syrup cautiously in diabetic patients, as it is a source of carbohydrates.

Fennel may interfere with the way the body processes certain drugs, herbs, or supplements using the liver's cytochrome P450 enzyme system. As a result, the levels of these agents may be increased in the blood, and may cause increased effects or potentially serious adverse reactions. Patients using any medications should check the package insert and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.

Use cautiously when taken by mouth in medicinal amounts for prolonged periods of time, as the constituent estragole is a procarcinogen (a substance that causes cancer after it is broken down by metabolic processes).

Use cautiously in patients using diuretics (agents that increase urination), immunosuppressants, or glaucoma agents.

Because fennel contains estrogen-like chemicals, the effects of other drugs, herbs, and supplements believed to have estrogen-like properties may be altered. Use cautiously in patients using hormone therapy or those with hormone-related disorders such as breast cancer or endometriosis, as fennel has been found to have estrogenic activity.

Use cautiously in patients taking ciprofloxacin or other quinolone antibiotics, as fennel may reduce their absorption.

Use cautiously, as fennel has been reported to be contaminated with Salmonella, Enterobacteriaceae, Serratia, Escherichia, and Yersinia enterocolitica. Cases of botulism have been reported following consumption of fennel.

Use cautiously, as accidental ingestion of 70% alcohol has been reported, due to similar packaging of fennel water and alcohol.

Avoid sweet fennel oil used as aromatherapy in seizure patients, according to the German Commission E monographs.

Avoid in individuals with a known allergy or hypersensitivity to fennel or other members of the Apiaceae plant family, including anise, carrot, celery, and mugwort, because of the chance of cross-sensitization. Severe laryngeal swelling, bronchial asthma, hives, or allergic shock may occur. Oral allergy syndrome has been reported with the use of fennel in a woman. Allergic reactions affecting the skin, such as atopic dermatitis (chronic skin inflammation) and light sensitivity, may occur in patients who consume fennel. Fennel has been reported to provoke reactions in children with food allergy.

Avoid fennel during pregnancy, due to a lack of safety and efficacy data.

Fennel may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants (blood thinners) such as warfarin (Coumadin®) or heparin, antiplatelet drugs such as clopidogrel (Plavix®), and nonsteroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).

Fennel may lower blood sugar levels. Caution is advised when using medications that may also lower blood sugar. Patients taking insulin or drugs for diabetes by mouth should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

Fennel may interfere with the way the body processes certain drugs using the liver's cytochrome P450 enzyme system. As a result, the levels of these drugs may be changed in the blood, and may cause increased or decreased effects or potentially serious adverse reactions. Patients using any medications should check the package insert and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.

Because fennel contains estrogen-like chemicals, the effects of drugs believed to have estrogen-like properties may be altered.

Use of fennel and ciprofloxacin (Cipro®) may lead to decreased bioavailability of ciprofloxacin. Theoretically, fennel may also interfere similarly with other fluoroquinolone antibiotics.

Although not well studied in humans, pretreatment with fennel essential oil may enhance the skin absorption of various topical agents, such as trazodone.

Fennel may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.

Fennel may lower blood sugar levels. Caution is advised when using herbs or supplements that may also lower blood sugar. Blood glucose levels may require monitoring, and doses may need adjustment.

Fennel may interfere with the way the body processes certain herbs or supplements using the liver's cytochrome P450 enzyme system. As a result, the levels of other herbs or supplements may become too high or too low in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.

Because fennel contains estrogen-like chemicals, the effects of herbs and supplements believed to have estrogen-like properties may be altered.

Although not well studied in humans, pretreatment with fennel essential oil may enhance the skin absorption of various topical agents.

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.